BIS(DIETHYLDITHIOCARBAMATO)NICKEL(~~)
Ivorganic Chemistry, Vol. 10, No. 6,1971 1141
CONTRIBUTION FROM CHEMICAL LABORATORY IV, DEPARTMENT OF PHYSICAL CHEMISTRY, H. C. ~ R S T E DINSTITUTE, COPENHAGEN, DENMARK
The Electronic Spectrum of Crystalline Bis(diethyldithiocarbamato)nickel(II) BY R. DINGLE*
Received September 14, 1970 Polarized crystal spectra reveal four weak absorption bands in the visible region of the spectrum of bis(N,N-diethyldithiocarbamato)nickel(II). On the basis of polarization and energy, the transitions involved are assigned as d-d, vibronically induced by a bsu vibrational mode. The suggested d-orbital ordering is d,, > d,a-,i > d,, > d,, > d,i. A brief discussion sf the vibronic coupling mechanism is given.
Gray and coworkers’ have made a thorough study of planar complexes in which d8 metal ions are bound to four sulfur atoms, the latter usually being part of two bidentate chelates of some complexity. Spectral, structural, magnetic, and molecular orbital investigations have led to plausible but unproven ordering schemes for the important molecular orbitals in these complexes. The large number of absorption bands of widely different character that occur in the electronic spectra provide a starting point from which to begin the unraveling of d-d, charge-transfer, and intraligand transitions. Even so, Gray, et al., have identified in their spectra only one or two of the four possible d-d transitions. One way actually to prove an assignment of an optical spectrum is to obtain crystal spectra and from the polarization behavior and other details to identify the ground and excited electronic states involved. For planar, diamagnetic complexes of d8 metal ions the ground state is universally accepted as lAlg, and hence only the excited electronic states are in need of identification. The present paper discusses crystal and solution spectra of some disubstituted dithiocarbamato complexes of nickel(I1). Experimental Section The complexes were prepared after the general method outlined by Cambi and Cagnasso.2 They were recrystallized from chloroform, benzene, or acetone, chemically analyzed, and oriented by X-ray methods. The crystals of the nickel complexes are dark green or black to the eye, but when thin sections are viewed in polarized light, they are bright green and orange in the two directions of extinction. Two Ni(I1) complexes have been studied in some detail; they are bis(N,N-diethy1dithiocarbamato)nickel(11) [hereafter Ni(DEDTC).J for which a complete crystal structural analysis is available and bis(N,N-dipropy1dithiocarbamato)nickel(I1) for which there are no crystallographic details available. Both crystals give very similar spectra. Solution spectra have been obtained in a variety of spectroscopic grade solvents using a Cary 14 spectrophotometer. Crystal spectra have been obtained using a microcrystal spectrometer attachmenta in conjunction with a Cary 14. All crystal spectral were obtained a t room temperature.
The Structure of Ni(DEDTC)2 The crystal structure of the stable a form of this
*
Address correspondence t o Bell Telephone Laboratories, Inc., Murray Hill, N. J. 07974. (1) S. I. Shupack, E. Billig, R. J. H. Clark, R. Williams, and H. B. Gray, J . Amev. Chem. Soc., 86, 4594 (1964), and earlier papers in this series; see also A, R. Latham, V. C. Hascall, and H. B. Gray, Inorg. Chem., 4, 788 (1965); R. W. Mason and H. B. Gray, ibcd., 7 , 55 (1968). (2) L. Cambi and A Cagnasso, A f t i Accad. N a z . Lincei, C l . Sci. F i s . , M a t . Natuv., Rend., 14, 71 (1931). (3) C. J. Ballhausen, N. Bjerrum, R. Dingle, K.Eriks, and C. R. Hare, Inoug. Chem., 4, 514 (1965).
complex has been determined by Shugam and Levina4 and by Bonamico, Dessy, Mariani, Vaciago, and Z a m b ~ n e l l i . ~The crystals are monoclinic, space group P 2 1 / c with the following unit cell dimensions : a = 6.19 8,b = 11.54 8, c = 11.60 8,@ = 95” 51’, and z = 2. The molecular units are planar and the molecular symmetry is D2h. From crystallographic and ire evidence an important canonical form is
i The crystals grown in the present study were very often twinned, and good, thin single crystals were hard to find. Those that were used usually had { O l l ) developed and they showed oblique extinction. Following the crystal structure, it is possible to project the molecules upon this face in order to establish the projections that the molecular axes make on the crystal extinction directions. The resultant absorption intensities with the molecular axes located as shown above are as follows: x polarized, green/orange, -10.0; y, green/orange, -0.3; z, green/orange, -
